1. Field of the Invention
The present invention relates to an apparatus for regulating a state of charge of cells of a battery set, which is preferably used for regulating a state of charge of each cell of a battery set for an electric automotive vehicle, for example.
2. Description of the Related Art
Conventionally, an apparatus has been proposed for regulating to uniform each of the states of charge of a plurality of secondary cells serially connected in a battery set. The state of charge of the secondary cell is shown as SOC and the secondary cell is shown as cell, hereinafter.
For example, in an apparatus disclosed in Japanese Patent Application Unexamined Laid-open publication No. 7-336905, a constant-voltage circuit having a constant voltage control section and a current saturation detecting section is provided so as to be connected in parallel with each of the cells constituting a battery set. Here, electric current is charged from a charger to the cells while bypassing a portion of the current in accordance with a difference between a voltage of each of the cells and a set voltage, the voltage of each of the cells is controlled using the constant-voltage circuit such that the voltage becomes equal to the set voltage, and the SOC of each of the cells are uniformly regulated.
More specifically, the flow of charging current to each of the cells is suppressed by bypassing in order of SOC having a higher value, and, to unsuppressed cells, all of the charging current is charged, because the charging current is not bypassed.
When the current saturation detecting section detects that the bypassed cell whose charging current is suppressed is saturated, a current reducing signal is sent to the charger in order to reduce the charging current.
Then, the charging current is reduced stepwisely by repeating the above operation, and when a predetermined minimum charging current is achieved, the charging of the cell is completed.
However, in such an apparatus, the constant-voltage circuit is operated to regulate the SOC in each of the cells just before the charging is completed, and in the case that the charging is not conducted until the predetermined minimum charging current is achieved before the charging is completed, the SOC of each of the cells can not be regulated sufficiently.
Further, in this apparatus, the charging current is suppressed by flowing great bypass current of about maximum 1(A) in a short time about 30 minutes. Therefore, a heating value of the constant-voltage circuit is great and it is necessary to provide a radiator of large volume.
Further, in this apparatus, to put it in an extreme way, the SOC is regulated by flowing the same charging current to each of the cells or by stopping the flow of the charging current, and for example, since a magnitude of electric amount (Ah) to be charged can not independently be varied for a cell except the electrically bypassed cell, it is difficult to precisely regulate the SOC for each of the cells with respect to a target SOC, and regulating precision is not excellent.